The present invention relates to the cleaning of surfaces such as the surfaces of cooking equipment, for example, ovens or broilers, which may be subject to heat and are liable to soiling by organic food deposits, especially baked-on organic food deposits. The soiling matter deposited on these surfaces typically consists of a complex mixture of natural fats and other organic deposits from the cooking of food. When heated at normal oven or broiler operating temperatures, this soiling matter may be converted into a polymeric mass in which part of the organic material may also be carbonized.
The removal of this type of soil is a considerable problem, especially in restaurants where ovens and broilers are used to cook large amounts of food and the resulting soil levels are high. Removal of badly burned soils requires the use of highly alkaline, unsafe oven cleaners (typically based on sodium or potassium hydroxide) and/or laborious scrubbing and scraping. The time, effort, and safety risk involved are such significant deterrents to regular cleaning, for example, on a daily basis, that restaurant ovens, broilers, and other surfaces liable to soiling by organic food deposits are often chronically soiled.
Oven cleaners containing alkali materials less alkaline than caustic soda are known. For example, U.S. Pat. No. 3,658,711 issued Apr. 25, 1972 to Mukai et al., and British Patent No. 1,275,740 published May 24, 1972 disclose the use of alkali metal phosphates combined with an amine component or "enhancing agent" and other optional ingredients such as, for example, surfactant, abrasives, thickening agents or suspending agents. However, such oven cleaners are not very effective in saponifying baked-on fat and, consequently, are not efficient oven cleaners. Further, such products, when applied to soiled oven surfaces, must attack the soiling matter from the outer surface, while the most severe polymerization and carbonization are generally present in the interior of the soil layer, adjacent to the oven wall.
In contrast to oven cleaners, oven pretreatment compositions which are applied to oven surfaces prior to soiling and then removed after soiling are also known. For instance, U.S. Pat. No. 4,877,691 to Cockrell discloses a composition comprising an inorganic thickening agent and an alkaline, water-soluble organic salt. The composition forms a food-safe coating which adheres to all portions of an oven surface and, in a clean oven, remains continuous as the coating dries. The resulting dried film is resistant to scuffing and chipping at typical oven temperatures and prevents fats and other food soils from burning onto exposed oven surfaces. After soiling, the film and the accompanying spattered food soils are easily removable by water or an aqueous solution.
The composition of U.S. Pat. No. 4,877,691, however, may not always remain adhered to surfaces which have already been soiled by organic food deposits, especially baked-on organic food deposits, which have not been removed in previous attempts to clean the surface. Thus, there is a need in the oven cleaning art for a pretreatment composition to be applied not only to a clean oven but also to an oven or broiler surface which may not be completely free from food soils when the composition is applied.
Further, the composition of U.S. Pat. No. 4,877,691 typically dries to form a film which may be hazy or opaque in appearance. This hazy or opaque appearance tends to obscure, at least to some extent, the original surface of the oven and may be considered aesthetically undesirable by some users. Thus, there has also been a need in the oven cleaning art for a pretreatment composition which, when applied to a desired surface to form a continuous coating, dries to form a substantially transparent film through which the original surface of the oven remains visible.